Hematopoiesis and Cellular Components of Blood

• Sites of Hematopoiesis

  • Embryonic liver and spleen

  • Bone marrow (extramedullary hematopoiesis)

• Stem Cells

  • Pluripotential stem cells develop into blood cells at various life stages (fetus, newborn, adult)

  • Types of stem cells:

    • Lymphoid stem cells

      • Differentiate into T cells (from thymus) and B cells

    • Myeloid stem cells

      • Erythroblasts

      • Megakaryoblasts (produce platelets)

      • Monoblasts (differentiate into monocytes)

      • Myeloblasts (differentiate into granulocytes)

• Types of Blood Cells

  • Erythrocytes (Red blood cells)

  • Leukocytes (White blood cells)

    • Granulocytes: Neutrophils, Eosinophils, Basophils

    • Lymphocytes: T lymphocytes, B lymphocytes, Natural killer cells

  • Platelets (Thrombocytes)

Microbiological Relationships

• Types of Relationships with Microorganisms

  • Symbiosis

    • Close and long-term biological interaction between two different species

  • Mutualism

    • Both species benefit

  • Commensalism

    • One species benefits, and the other is neither helped nor harmed

  • Pathogenicity

    • The capacity of microorganisms to cause disease

  • Opportunism

    • Pathogens that cause disease predominantly in immunocompromised hosts

• Normal Microbiome

  • Comprises symbiotic microorganisms that inhabit the human body

Infection Process Overview

1. Encounter

   • Routes of exposure: Endogenous and Exogenous microorganisms

2. Transmission

   • Direct (contact-based) or Indirect (via surfaces or vector)

3. Colonization

   • Surviving and multiplying in the human environmental conditions

4. Invasion

   • Breaching physical barriers to penetrate tissues

5. Dissemination

   • Spreading infection throughout the body

6. Damage

   • Cellular/Damage Mechanisms:

     • Direct damage by toxins

     • Indirect damage using immune responses features

Factors Influencing Infection

• Communicability

  • Ability to spread from individual to individual

• Immunogenicity

  • Ability to stimulate an immune response

• Infectivity

  • How pathogens invade and multiply

• Toxigenicity

  • Capability of producing toxins

• Virulence

  • Severity of the disease caused by the agent

Stages of Infection

1. Incubation Period

   • Time from exposure to onset of symptoms; pathogens establish colonization

2. Prodromal Stage

   • Initial symptoms (often mild); pathogens proliferate

3. Invasion or Acute Illness

   • Major immune and inflammatory responses activate; pathogens rapidly multiply

4. Convalescence

   • Symptoms diminish; body's defenses remove pathogens, but may enter latency or cause fatality in severe cases

Biochemical and Mechanical Barriers

• Primary Barriers:

  • Lysozyme in secretions

  • Mucus in trachea

  • Cilia and skin

  • Acid in stomach and flora in gut

Transmission and Prevention Strategies

• Chain of Transmission:

  • Interfaces between reservoir, portal of exit, mode of transmission, portal of entry, and susceptible victim

  • Interventions include vaccine usage, personal hygiene measures like handwashing, and needle sterilization

Bacterial Disease Overview

• Characteristics of Bacteria:

  • Prokaryotic nature (no nucleus)

  • Classification based on oxygen requirements and Gram staining (Gram-positive/Gram-negative)

  • Example: Staphylococcus aureus infection

• Virulence Factors:

  • Include pili, flagella, capsules, enzymes, iron/nutrient competition, and toxins

Viral Disease Characteristics

• Common viruses impact humans and can be transmitted through several means, including aerosols and infected fluid.

• The life cycle consists of attachment, penetration, uncoating, replication, assembly, and release

• Effects on host: inhibition of cell processes, fusion of cells, and potential transformation to malignancy.

• Viral agents vary in their strategies by inducing altered immulogic responses, including antigenic variation to escape detection

Fungal Infection Characteristics

• Fungi Structure:

  • Eukaryotic with rigid cell walls; exist as yeasts or molds

• Diseases: Result from pathogenic fungi, with dermatophytes causing superficial infections (tinea) while Candida albicans causes opportunistic infections, particularly in immunocompromised individuals

Key Components of the Immune System

• Primary and Secondary Lymphoid Organs: Contains bone marrow, thymus, spleen, lymph nodes, and Peyer patches

• Key Immune Cells:

  • Lymphocytes: T cells (helper/cytotoxic), B cells (antibody production), Natural killer cells

  • Phagocytic Cells: Monocytes and macrophages

• Components of Immune Response:

  • Antibodies function in neutralizing pathogens, and cytokines mediate response adaptations.

Immune System Functions

• Macrophages: Key in recognizing and eliminating pathogens

• B-Cell Response: Differentiation into plasma cells for specific antibody production and formation of memory cells for future immune reactions

• T-Cell Activation: Regulates immune response and provides cytotoxic effects on infected cells.

Immunity and Tolerance

• Autoimmunity: Misidentifying self-antigens as foreign, leading to chronic inflammatory and autoimmune diseases

• Hypersensitivity Reactions: Overreactions of immune mechanisms that can cause tissue damage; categorized into four distinct types based on mechanisms and symptoms.

Immune Deficiencies Overview

• Congenital (primary) and acquired (secondary) deficiencies disrupt normal immune function leading to increased infection susceptibility. Management involves monitoring and specific treatments based on the involved lineage of immune cells.